Chemistry 1251 Practice Exam 4 PDF

A Chemistry 1251 Exam #4 (75 minutes) April 22, 2024 First Name Last Name Signature ________...

A Chemistry 1251 Exam #4 (75 minutes) April 22, 2024 First Name Last Name Signature ________ SID# 80 You must sign here to affirm that you are adhering to the UNCC Student Code of Academic Integrity. Please check the section in which you are enrolled: Michael (001) MWF 8:00 AM _______ Black (003) TR 10:00 AM _______ White (002) MWF 10:10 AM _______ Black (004) TR 2:30 PM _______ Please read all questions carefully and answer them completely and clearly. The exam packet should have 10 pages for a total of 20 questions. The last page is the answer sheet, where you will record all of your responses. The next to last page is the Exam Information Sheet. Individual point values for free response questions are given beside each question. You are encouraged to write in the exam packet, but only the responses that you record on the Gradescope answer sheet will be graded. If you continue to write or bubble after time is called, you will automatically receive a zero for your grade. There are no bathroom breaks; when you leave the room, you must surrender all of your exam materials for grading. 1  A Multiple Choice Instructions: Bubble the letter that corresponds to the best answer for each question on your Gradescope answer sheet. Any answers for questions 1 – 16 recorded on these pages will not be graded. Each question is worth 4 points. 1. How many moles of NH3 would be required to react with 0.470 moles of copper(II) oxide in the following chemical reaction? 2 NH3 (g) + 3 CuO (s) → 3 Cu (s) + N2 (g) + 3 H2O (g) (A) 0.470 mol NH3 (B) 0.705 mol NH3 (C) 0.940 mol NH3 (D) 1.41 mol NH3 (E) 0.313 mol NH3 2. A chemist performs a chemical reaction and collects 1.25 g of the product. If they calculated a 63.5% yield, what was the theoretical yield for their reaction? (A) 0.794 g (B) 0.456 g (C) 3.42 g (D) 1.97 g (E) 2.04 g 3. Consider the following balanced equation: 3 H2 (g) + N2 (g) → 2 NH3 (g) If the reaction is performed with each of the following sets of initial amounts of the reactants, in which case is N2 the limiting reactant? (A) 5.00 mol H2 and 5.00 mol N2 (B) 35 mol H2 and 15 mol N2 (C) 4.5 x 10-4 mol H2 and 1.5 x 10-3 mol N2 (D) 2.0 mol H2 and 0.65 mol N2 (E) N2 is always the limiting reactant. 4. If 8.00 moles of Xe and 10.0 moles of F2 react to form XeF4 , what do you expect to be in the reaction flask at the end of the reaction if it goes to completion? Xe (g) + 2 F2 (g) → XeF4 (g) (A) Only XeF4 (B) Xe and XeF4 (C) F2 and XeF4 (D) Xe, F2 , and XeF4 2  A 5. The drawing below shows a mixture of molecules: Suppose the following reaction can take place in this mixture: CO(𝑔𝑔) + 2 H2 (𝑔𝑔) → CH3 OH(𝑔𝑔) Which reactant is in excess, and how many reactant molecules would be left over after the reaction goes to completion? (A) CO is the reactant in excess, and there would be one molecule left over. (B) H2 is the reactant in excess, and there would be one molecule left over. (C) CH3OH is the reactant in excess, and there would be three molecules left over. (D) CO is the reactant in excess, and there would be four molecules left over. (E) There is no limiting reactant in this situation, both reactants would be completely consumed. 6. A student needs 0.300 mol of silver perchlorate for an experiment. The student has access to a 13.0 M silver perchlorate solution. How many liters of the solution should the student use for their experiment? (A) 43.3 L (B) 0.0231 L (C) 3.90 L (D) 809 L (E) 4.79 L 7. A lab experiment calls for 49.1 g of Ba(ClO3)2 to be dissolved in water to make a total solution volume of 0.200 L. What is the molarity of the final solution? (A) 0.807 M (B) 74700 M (C) 0.913 M (D) 0.0322 M (E) 1.24 M 3  A 8. A brand new student in Dr. Troutman’s biochemistry lab is instructed to prepare 50.00 mL of a 2.00 M calcium chloride solution from a 9.87 M stock solution and as much water as needed. The student seems a little confused, but Dr. Troutman insists the student was taught how to do this in CHEM 1251 and leaves the student alone to figure out the process. Describe how the student should go about preparing the solution. (A) Add 10.1 mL of the CaCl2 stock solution to a flask then add 50.00 mL of water. (B) Add 247 mL of the CaCl2 stock solution to a flask then add 226 mL of water. (C) Pour all of the stock solution into the largest flask you can find, then add an equal amount of water. (D) Add 0.395 mL of the CaCl2 stock solution to a flask then fill to 50.00 mL with water. (E) Add 10.1 mL of the CaCl2 stock solution to a flask then fill with water to 50.00 mL total volume. 9. Which of the following solutions would have the highest concentration of H+ ions? (A) 0.7 M CH4 (B) 0.7 M HCl (C) 0.8 M Ba(OH)2 (D) 0.3 M H2SO4 (E) 0.3 M (NH4)2S 10. Both species A and B are soluble in water. Based on the representations of the species in and out of solution below, which of the following statements are true? (A) Both solutions A and B would conduct electricity. (B) Only solution A would conduct electricity. (C) Only solution B would conduct electricity. (D) Neither solution A nor B would conduct electricity. 11. Which of the following compounds is soluble in water? (A) PbBr2 (B) AgI (C) NH4OH (D) MgCrO4 (E) Ca3(PO4)2 4  A 12. What are the spectator ions in the reaction that occurs when aqueous solutions of copper(II) nitrate and sodium phosphate are combined? (A) Cu2+ and PO43- (B) Na+ and PO43- (C) NO3⁻ and Cu2+ (D) All of the ions are spectator ions. (E) Na+ and NO3⁻ 13. What is the net ionic equation for the reaction, if any, that occurs when aqueous solutions of potassium carbonate and magnesium sulfate are combined? (A) No reaction (NR) (B) Mg2+ (aq) + CO32- (aq) → MgCO3 (s) (C) 2K+ (aq) + SO42- (aq) → K2SO4 (s) (D) Mg2+ (aq) + SO42- (aq) → MgSO4 (s) (E) K2+ (aq) + CO32- (aq) → K2CO3 (s) 14. Which of the following statements regarding oxidation states is FALSE? (A) The oxidation state of nitrogen in N2 is 0. (B) The oxidation state of calcium in calcium oxide is +2. (C) The oxidation state of copper in Cu2O is +1. (D) The oxidation state of chlorine in the chlorite ion is -1. (E) The oxidation state of boron in B2H6 is -3. 15. In the reaction 2 Al (s) + 3 FeCl2 (aq) → 3 Fe (s) + 2 AlCl3 (aq), (A) Al is oxidized and Fe is reduced. (B) Al is oxidized and Cl is reduced. (C) Cl is oxidized and Fe is reduced. (D) Fe is oxidized and Al is reduced. (E) Fe is oxidized and Cl is reduced. 16. In a portion of a redox reaction, SO42- changes to SO2. In this reaction, each sulfur atom (A) gains 1 electron. (B) gains 2 electrons. (C) loses 1 electron. (D) neither gains nor loses electrons. (E) loses 2 electrons. The short answer and free response questions (17 - 20) appear on the front AND BACK of your Gradescope Answer sheet. Record your responses on the Gradescope sheet, not your exam booklet. Follow the instructions carefully to include any work that might be required for full credit with a specific question. 5  Useful Constants Avogadro’s Number (N) 6.022 x 1023 /mol Mass of electron 9.109  10–28 g Specific heat of H2O (l) 4.184 J/(g · °C) Mass of neutron 1.675  10–24 g Planck’s constant (h) 6.63  10–34 J · s Mass of proton 1.673  10–24 g Speed of light in a vacuum (c) 3.00  108 m/s Electron charge 1.602  10–19 C Conversion Factors 1 cm3 = 1 mL giga (G) = 109 1 Hz = 1 s-1 mega (M) = 106 TC = (TF – 32 °F) x (5°C)/(9°F) kilo (k) = 103 TK = TC + 273.15 deci (d) = 10–1 1 amu = 1.66 x 10-24 g centi (c) = 10–2 1 cal = 4.184 J milli (m) = 10–3 1J = 1N·m micro (μ) = 10–6 1 N = 1 kg · m nano (n) = 10–9 s2 1 J = 1 kg · m2 pico (p) = 10–12 s2 1 Angstrom (Å) = 10–10 m femto (f) = 10–15 Formulas Formulas ℎ𝑐 1 𝑐= 𝜆𝜈 𝐸 =ℎ𝜈= 𝐸𝑛 = −2.18 ∙ 10−18 𝐽 ( 2 ) Δ𝐸 = 𝐸𝑓𝑖𝑛𝑎𝑙 − 𝐸𝑖𝑛𝑖𝑡𝑖𝑎𝑙 𝜆 𝑛 𝑘 𝑄1 𝑄2 𝐸= ∆𝑈 = 𝑞 + 𝑤 𝑑 𝑛 ∆𝐻𝑟𝑥𝑛 = 𝑞𝑟𝑥𝑛 𝑞𝑟𝑥𝑛 = − 𝑠𝑠𝑜𝑙𝑛 ∙ 𝑚𝑠𝑜𝑙𝑛 ∙ ∆𝑇𝑠𝑜𝑙𝑛 𝑞 = 𝑠 𝑚 ∆𝑇 0 Δ𝐻𝑟𝑥𝑛 = Σ 𝑛 Δ𝐻𝑓𝑜 (𝑝𝑟𝑜𝑑𝑢𝑐𝑡𝑠) − Σ 𝑛 Δ𝐻𝑓𝑜 (𝑟𝑒𝑎𝑐𝑡𝑎𝑛𝑡𝑠) 𝑜 Δ𝐻𝑟𝑥𝑛 = Σ (𝑒𝑛𝑡ℎ𝑎𝑙𝑝𝑖𝑒𝑠 𝑜𝑓 𝑏𝑜𝑛𝑑𝑠 𝑏𝑟𝑜𝑘𝑒𝑛) − Σ (𝑒𝑛𝑡ℎ𝑎𝑙𝑝𝑖𝑒𝑠 𝑜𝑓 𝑏𝑜𝑛𝑑𝑠 𝑓𝑜𝑟𝑚𝑒𝑑) Solubility Rules: 1. Most nitrate, chlorate, and acetate salts are soluble. 2. Most salts of alkali metals and ammonium cations are soluble. 3. Most chloride, bromide, and iodide salts are soluble. Exceptions: Salts containing Ag+, Pb2+, and Hg22+ ions are insoluble. 4. Most sulfate salts are soluble. Exceptions: Sulfates containing Ag+, Ca2+, Sr2+, Ba2+, Pb2+ and Hg22+ ions are insoluble. 5. Most hydroxide salts are insoluble. Exceptions: Salts containing Ba2+, alkali metals, and ammonium cations are soluble. 6. Most carbonate, chromate, phosphate and sulfide salts are insoluble. Exceptions: Salts of alkali metal and ammonium cations are soluble. CHEM 1251 Spring 2024 Exam 4 Version A Answer Sheet Name ID A B C D E Short Answer Questions: Fill in the blanks provided with the correct 1 A response. 2 A 17. (a) Balance the chemical equation below using the smallest possible 3 A whole number stoichiometric coefficients. Place a number in each box. 4 A (+3 pts) 5 A H2 (g) + P4 (s) → PH3(g) 6 A (b) Write the balanced chemical equation for the combustion of gaseous 7 A butane (C4H10), using the smallest, whole number coefficients. Include 8 A physical states of the reactants and products. (+4 pts) 9 A 10 A 11 A 12 A (c) Write the balanced molecular equation for the reaction that occurs 13 A when aqueous solutions of barium hydroxide (barium = Ba) and nitric acid 14 A (HNO3) are combined. Use the smallest, whole number coefficients and include physical states of the reactants and products. (+5 pts) 15 A 16 A Show ALL of your work for questions 18 – 20 using dimensional analysis in the space provided. Include all units and round the final answer to the correct number of significant figures. Scientific notation should be shown using 10x, not “E” notation. All constants must be shown as their numerical values with units. 18. A chemist prepares a solution of magnesium fluoride by measuring out 0.0315 µmol of magnesium fluoride into a 400.0 mL volumetric flask and filling the flask to the mark with water. Calculate the molarity of the final solution. (+8 pts) Complete questions 19 and 20 on the back of this page. CHEM 1251 Spring 2024 Exam 4 Version A Answer Sheet Name: __________________________________________________________ Show ALL of your work using dimensional analysis in the space provided. Include all units and round the final answer to the correct number of significant figures. Scientific notation should be shown using 10x, not “E” notation. All constants must be shown as their numerical values with units. 19. A student must determine the concentration of H2SO4 in a solution from a car battery. The student finds that 15.49 mL of 0.150 M NaOH is needed to reach the equivalence point with 25.00 mL of the battery solution. What is the molarity of H2SO4 in the battery solution? (+8 pts) 20. If 20.0 g of NaOH is added to excess Cd(NO3)2 solution, what mass of precipitate will be formed in the following reaction? (+8 pts) 2 NaOH (aq) + Cd(NO3)2 (aq) → Cd(OH)2 (s) + 2 NaNO3 (aq)